Five Catalan separatist politicians – currently on trial accused of rebellion – are poised to take their seats in the Spanish parliament under police escort.
It is the first time that Spain has admitted elected detainees into parliament. The move was denounced by Catalan separatist leader Carles Puigdemont, a fugitive in Belgium.
Four of the Catalans are lower-house MPs and one is a senator.
After being sworn in they are expected to be returned to prison.
They won seats in the Spanish general election on 28 April which was won by the Socialists but without a majority.
Conservative Popular Party (PP) and centre-right Ciudadanos MPs say they will try to get the separatists suspended from parliament. That would prevent them taking their seats.
The five are on trial for taking part in Catalonia’s push for independence in 2017.
The five are: MPs Josep Rull, Oriol Junqueras, Jordi Sànchez, Jordi Turull and senator Raül Romeva.